Vinyl ester resin and process for curing same with ionizing radiation in the presence of amines

ABSTRACT

The addition of about 1.5 to 5 weight percent of certain amines to a thermosettable mixture of a nonvolatile vinyl monomer and a polymerizable vinyl ester resin reduces the dosage level of ionizing radiation required to cure the mixture.

United States Patent 11 1 Mani 1451 Aug. 26, 1975 1 1 VINYL ESTER RESIN AND PROCESS FOR CURING SAME WITH IONIZING RADIATION IN THE PRESENCE OF AMINES [75] Inventor: Inder Mani, Midland, Mich.

[73] Assignec: The Dow Chemical Company,

Midland, Mich.

[22] Filed: Aug. 27, I973 [21] Appli No.: 391,691

Related US. Application Data [62] Division of Scr. No. 143,268, May 13, 1971, Pat No.

[52] US. Cl 204/l59.16; 117/9331; 117/132 B; 117/132 BE; 117/161 ZB; 117/161 UZ;

[51] Int. Cl. 1. C08d 1/00; C08f 1/00 [58] Field of SearchHH. 204/159.15, 159.19, 159.16; 260/836, 837 R Primary ExaminerMurray Tillman Assistant Examiner-Richard B. Turer Attorney, Agent, or Firm-H. L. Aamoth [57] ABSTRACT The addition of about 1.5 to 5 weight percent of cer tain amines to a thermosettable mixture of a nonvolatile vinyl monomer and a polymerizable vinyl ester resin reduces the dosage level of ionizing radiation required to cure the mixture.

4 Claims, No Drawings VINYL ESTER RESIN AND PROCESS FOR CURING SAME WITH IONIZING RADIATION IN THE PRESENCE OF AMINES CROSS-RFFERFNCF. TO RELATED APPLICATION This is a division of application Ser. No. M3268 filed May l3. l97l. now US. Pat. No. lblllfllo.

BACKGROUND OF IHF. INVENTION Ihis invention relates to the field of ioni7ing radiation cure of polymcri/ablc materials and to coatings of same and especially relates to a promoter to reduce the ioniling radiation level or dosage necessary to effect a cure of said materials.

From a commercial standpoint radiation curing offers a number of advantages over thermal catalystinitiated cures". immediate initiation of polymerization. evtended pot-life of the curable materials. little temperature rise so heat sensitive substrates may be employ ed in coatings. better control of the polymerization reaction. superior substrate-coating bonds are produced and much higher concentration of radicals may be produced instantaneously. However. these advantages are difficult to realive if the curable materials require high curing doses of ioni/ing radiation since the economics become prohibitive. Comrnerialilation then depends on reducing the cost of the curing process by finding methods and materials to effect a care at lower dosages.

The search for means to accelerate or promote radiation curing is evident by a number of patents relating to certain polynierirable materials. While neither the promoters or the polymerizable materials employed correspond in any way to this invention. patents representative of such efforts include US. Pat. Nos. 3.202.5l3; 3.251.759; 3.265.hll4; 3.352.771 and 2.979.446. Commercially it is desirable to be able to cure at dosages of no more than 2 to 3 megarads but it would be of great advantage to be able to cure at l mcgarad and preferably even less.

SIMMARY OF IHF INVENTION According to this invention the curing dosage of ioni7ing radiation required to cure in an inert atmosphere a mixture of a nonvolatile vinyl monomer and a poly meri/able \in \l ester resin is reduced by adding to the mixture at least 0.3 weight percent of certain nitrogen containing materials.

I'hc \inyl cster resin is prepared by reacting about equivalent amounts of a dicarboxylic acid half ester having the formula herein R is hydrogen or an alkyl group of l to 4 car bons. R: is an alky lcne group of Z to (I carbons and R is phenylene. cyclohe\ \lenc. alkylene or an unsaturated bivalent hydrocarbon radical. \\ith a polyeposidc of a polyhydric phenol ha\ ing more than one epovide group per molecule. l'he nitrogen materials include arious l-oxa/olincs. guanidincs and certain amines which are more fully described hereafter.

(ill

DESCRIPTION OF THE INVENTION The general methods by which vinyl ester resins may be prepared are thoroughly described in the patent literature. Representative patents which describe the resins and their preparation include US Pat. Nos. 3.066.112; 3.179.623; 3.256.226; 3.301.743 and 3.377.406.

In particular the vinyl ester resins employed in this invention are described in US Pat. No. 3.367.992 along with methods for their preparation. More particularly this invention relates to said resins prepared from polyepoxides of polyhydric phenols having more than one epoxide group per molecule.

The vinyl ester resins are prepared by reaction of cssentially equivalent amounts of said polyepoxide of a polyhydric phenol and a dicarboxylic acid half ester having the formula 0 0 o It ll ll where R, is hydrogen or an alkyl group of l to 4 carbons. R is an alkylene group of 2 to 6 carbons and R is phenylene, cyclohexylene. alkylene or an unsaturated bivalent hydrocarbon radical.

Said halfesters are conveniently prepared by esterification of a hydroxyalkyl acrylate or methacrylate with an equal molar amount of a dicarboxylic acid. or prel erably a dicarboxylic acid anhydride where it evists. For example. equal molar amounts of lhydroxyethyl acrylate and maleic anhydride may be reacted to form said half ester. Accordingly R, in the formula is usually hydrogen or methyl. In place of Z-hydroxyethyl acry late one may employ hydroxypropyl or hydroxybutyl acrylate or methacrylate. Also. in place of maleic anhy dride or maleic acid one may employ fumaric acid. itaconic acid. citraconic acid. adipic acid. the isomeric phthalic acids and the like. The anhydrides of said acids. where available. may also be used.

Said half ester is reacted with a polyepoxide of a poly hydric phenol wherein the polyepoxide has an ep oxide equivalent weight of about I50 up to 1000 and even higher. Said polyepoxides are made by reacting at least about two moles of an epihalohydrin. such as epichlorohydrin. with one mole of a polyhydric phenol and a sufficient amount of an alkali to combine with the halogen of the halohydrin. Polyhydric phenols include the familiar bisphcnol A as well as p.p'- dihydroxydiphenyl. p.p'-dihydroxyphenyl sulfone. p.p-dihydroxybenzophenone. p.p'dihydroxydisphenylmethane. the various other position isomers of the above polyhydric phenols. polyhydric phenolic formaldehyde condensation products (novolac resins] and the like. Mononuclear phenols such as resorcinol. catechol. hydroquinonc. phloroglucinol and the like may also be employed. The polyepoxides are charac- ICI'IYCLI in having more than one cpovide group per mol ecule.

\arious catalysts may be used in the preparation of vinyl ester resins. Catalysts include tertiary amines such as tristdimethylaminomethyl)phenol. onium catalysts. triphenyl stibine and triphenyl phosphine and the like. Usually hydroquinone or other like polymerization in hibitors are added to prev ent poly mcriration during the preparation of the resin.

According to this invention the poly meri/able mate rials comprise a mixture of said vinyl ester resin with a copolymeri/able vinyl monomer which is non\olatile. By nonvolatile it is meant to exclude monomers which are predominantly gases at ambient temperatures. It is oby ious that if the monomer is too volatile a substantial portion of the monomer would evaporate from a film or coating before the mixture of monomer and resin could be cured. Monomers which are normally liquid at room temperature may be used even though there may be a small loss of monomer by evaporation lt is possible to operate the process of this invention under higher pressures than atmospheric pressure to minimize any loss of said normally liquid monomers.

Nonvolatile vinyl monomers which may be employed with this invention include both mono-and polyunsaturated monomers. Polymerizable monounsaturated acids include alkenyl aromatic monomers such as styrene. vinyl toluene. chlorostyrcnes and the like; vinyl carboxylic acids such as acrylic and methacrylic acid; vinyl nitriles such as acrylonitrile and methacrylonitrile'. alkyl and hydroxyalkyl esters ofvinyl carboxylic acids. wherein the alkyl groups contains from I to U carbons. such as methyl acrylate. butyl acrylate. methyl ester of cinnamic acid. cyclohexyl methacrylate. hydroxyethyl methacrylate. hydroxypropyl acrylate hy droxybutyl acrylate and the like; vinyl amide monomers such as acryarnide. diacetone acrylamide and the like; or mixtures thereof.

A variety of polyunsaturated polymerizable monomers within the above classes may be used including ethylene glycol dimethacrylate. trimethylol propane trimethacrylate. methylene bisacrylamide and other similar monomers.

The polymerizablc materials of this invention are especially useful in coating various substrates such as metal. wood and the like either as a primer coating andor a finished coating. ln order to obtain the benefits of this invention at least 0.3 weight percent of the nitrogen containing material is added to the polymeriyable materials. While quite large amounts of the nitrogen containing material may be added there is no advantage in doing so. Preferably the amount ranges from about ()5 to 10 weight percent and most preferably from about l.5 to 5 weight percent.

When employed as coating formulations other addi tives may be incorporated into the coating. for example. various inert fillers and pigments such as kaolin clay. titanium dioxide. silica. various inorganic oxides and the like. Films cast from the coating formulations may be rapidly cured by exposing them in an inert atmosphere to ionizing radiation (accelerated particulate radiation). A beam intensity of at least it) microamperes is usually employed. but this invention is not lim ited thereto and lower beam intensities may be employed.

Generally the films or coatings will range in thickness from about 0.1 mil up to about 10 mils. However. de pending on the accelerating voltage. thicknesses up to 251) mils or higher are feasible. The radiation curing step should be performed in an inert atmosphere. By this it is meant an atmosphere which is essentially free ofoxygcn since the presence of oxygen may result in an undesirable tacky surface. It is suflicient for this purpose to place a thin film of a plastic material such as a polyester (Mylar) film on the cast film or coating. Other means may be used such as curing in a chamber containing an essentially osygen free atmosphere such as nitrogen. helium. argon and the like.

Accelerated particulate (ionizing) radiation includes particles such as electrons. protons. deuterons. other ions and the like. However. from an industrial standpoint. the cost and availability of machines limit ioni7- ing radiation curing to accelerated electrons for the im mediate future. A variety of devices are available to provide accelerated electron radiation or varying voltages and beam intensities. Typical of such devices is the familiar Van de (iraaf accelerator. Similar commercial accelerators utili7ing various acceleration means are available from Texas Nuclear Corporation. (cascade rectified system) High Voltage Engineering. (insulated core transformer system) General Electric (a resonant transformer design) and Radiation Dynamics. Inc. (radio frequency cascade rectifier system).

Nitrogen containing materials include Z-oxazolines. guanidines and certain amines. Typical of the Z oxazolines are Z-oxazoline itself. and substituted 2- oxa7olines having the formula (1 wherein R and R" may be hydrogen. methyl. ethyl. phenyl and the like. R may be an alkyl. aryl. aralkyl group or H. Such substituted oxa/olines include Z-methyl-Z-oxa7olinc. 3.5-diphcnylQ-oxayoline; Z- phenyl. S-methyl-loxazoline; Z-methyl. 5 phenyl-2- oxayoline and the like. Also included within the term Z-oxazolines are the his osayolines such as 1.2- tetramethylene bisllosayoline). ll osydiethylene hisQ-oxazoline; Z.Z'thiodiethylene bisl Z-oxa7oline) and the like. Guanidines include guanidine. tetramethyl guanidine and the like.

Amines which may be employed have the formula R R R N wherein R may be an alkyl or an aralkyl group. R and R each may be hydrogen or an alkyl group or R and R together may be a cyclic alkylcne radical or an oxydialkylene radical. Alkyl groups in clude methyl. ethyl propyl. n-hutyl. isobutyl and higher alkyl groups. Typical amines include mono. diand trin-butyl amine. di-isobutyl amine. triethyl amine. cyclohexylamine. benyyl amine. morpholine. piperidine and the like.

The following non-limiting examples will further illtistrate the invention. All parts and percentages are by weight unless otherwise specified.

EXAMPLE l A vinyl ester resin v as prepared by reacting 2- hydroxyethyl acrylate (30.5%) with maleic anhydride (25% to form a half ester which was subsequently re acted with a glycidyl polycther of bisphenol A having an epoxide equivalent weight (FEW) of lRh-WZ (D.F..R. 33l according to the procedure of L'.S. Pat. No. 3.367.992. The resin was then mixed with a monomer in the weight proportion of Z/l respectively. The monomer of Resin A-l \vas n butyl acrylate and the monomer of Resin Bl was sty rcne. The monomer of Resin (-l was ccllosolve acrylate (Ml/40). To these mixtures was added 3'; of unions nitrogen containing connionnds.

A film was cast from each of the resin mixtures with a 7 mil draw-down bar on a O-panel (4 inches l2 inches X (1.03 inch) and covered with a 2 mil sheet of Mylar (polyester) film to exclude air. The coated polished steel panel was then passed through a 2 Mev electron beam from a Van de Graaf accelerator filtered with (1.33 gm/cm Al. A 50 microampere beam current and a conveyor speed of 3.4 cm/sec delivered a dose of (1.1 Megarad (Mr-ad) for each pass through the beam.

The curing dose in megarads (Mr-ad) for each of the coated panels is shown below.

When the resin of the previous example was mixed with Z-hydroxyethyl acrylate (1/1). The mixture required 0.4 Mrad to cure. The addition of 3% of dibutyl amine reduced the curing dose to (1. l5 Mrad.

EXAMPLE 3 Using Resin Al the dosage to cure was determined with varying amounts of di-n-butyl amine according to the procedure of Example I.

di-n'hulyl amine Resin A-l None (1.'-1-l.() Mrad The tests showed at least about 0.371 is necessary. A minimum is found in the range of about 1.5 to 571 and no advantage is found above about 1071.

EXAMPLE 4 A vinyl ester resin was prepared by reacting 2- hydroxyethyl acrylate (25.55%) with phthalic anhydride (32.69?) to form a half ester. The half ester was then reacted with D.E.R. 33] (4l.ii5%) to form the vinyl ester resin which was then mixed with a monomer in the proportions of 2/] as before. Resin A-4 contained n butyl acrylate and Resin B-4 contained styrene. Films were cast and cured by the procedure of Example I.

It will be understood that the present invention is not limited to the specific details described above but may embody various modifications insofar as they are defined in the following claims.

What is claimed is:

l. A process for curing a mixture of a polymerizable vinyl ester resin and a nonvolatile vinyl monomer se' lected from the group consisting of alkenyl aromatics. vinyl carboxylic acids. vinyl nitriles. vinyl amides. alkyl and hydroxyalkyl esters of vinyl carboxylic acids wherein the alkyl group contains from I to 8 carbons. and mixtures thereof. said process comprises exposing said thermosettable mixture in an inert atmosphere to ionizing radiation. said mixture having added thereto about 1.5 to 5 weight percent based on the weight of the mixture of an amine having the formula R R. .R;.N where R is an alkyl or arallzyl group. R. is hydrogen and R may be hydrogen or an alkyl group or R and R together may be a cyclic alkylene radical or an oxydialkylene radical; and wherein said vinyl ester resin is prepared by reacting about equivalent amounts of a polyepoxide of a polyhydric phenol having more than one epoxide group per molecule with a dicarboxylic acid half ester having the formula where R, is hydrogen or an alkyl group of l to 4 carbons, R is an alkylene group of 2 to 6 carbons and R. is phenylene. cyclohexylene. alkylene or an unsaturated bivalent hydrocarbon radical.

2. The process of claim I wherein R in the amine formula is hydrogen.

3. A thermosettable mixture suitable for curing by exposure to low levels of ionizing radiation comprising a mixture of a polymerizable vinyl ester resin and a nonvolatile monomer selected from the group consisting of alkenyl aromatics. vinyl earboxylic acids. vinyl nitriles. vinyl amides. alkyl and hydroxyalkyl esters of vinyl carboxylic acids wherein the alkyl group contains from l to 8 carbons. and mixtures thereof. said thermosettable mixture have added thereto about 1.5 to 5 weight percent based on the weight of the mixture of an amine having the formula R,R R;.N where R is an alkyl or aralkyl group. R. is hydrogen and R;. may be hydrogen or an alkyl group or R. and R together may be a cyclic alkylene radical or an oxydialkylene radical; and wherein said vinyl ester resin is prepared by react ing about equivalent amounts of a polyepoxide of a polyhydric phenol having more than one epoxide group per molecule with u dicarhoxylic acid hull cstcr halving the formula 

1. A PROCESS FOR CURING A MIXTURE OF A POLYMERIZABLE VINYL ESTER RESIN AND A NONVOLATILE VINYL MONOMER SELECTED FROM THE GROUP CONSISTING OF ALKENYL AROMATICS, VINYL CARBOXYLIC ACIDS, VINYL NITRILES, VINYL AMIDES, ALKYL AND HYDROXYALKYL ESTERS OF VINYL CARBOXYLIC ACIDS WHEREIN THE ALKYL GROUP CONTAINS FROM 1 TO 8 CARBONS, AND MIXTURES THEREOF, SAID PROCESS COMPRISES EXPOSING SAID THERMOSETTABLE MIXTURE IN AN INERT ATMOSPHERE TO IONIZING RADIATION, SAID MIXTURE HAVING ADDED THERETO ABOUT 1.5 TO 5 WEIGHT PERCENT BASED ON THE WEIGHT OF THE MIXTURE OF AN AMINE HAVING THE FORMULA R1R2R3N WHERE R1 IS AN ALKYL OR ARALKYL GROUP, R2 IS HYDROGEN AND R3 MAY BE HYDROGEN OR AN ALKYL GROUP OR R1 AND R3 TOGTHER MAY BE A CYCLIC ALKYLENE RADICAL OR AN OXYDIALKYLENE RADICAL, AND WHEREIN SAID VINYL ESTER RESIN IS PREPARED BY REACTING ABOUT EQUIVALENT AMOUNTS OF A POLYEPOXIDE OF A POLYHYDRIC PHENOL HAVING MORE THAN ONE EPOXIDE GROUP PER MOLECULE WITH A DICARBOXYLIC ACID HALF ESTER HAVING THE FORMULA
 2. The process of claim 1 wherein R3 in the amine formula is hydrogen.
 3. A thermosettable mixture suitable for curing by exposure to low levels of ionizing radiation comprising a mixture of a polymerizable vinyl ester resin and a nonvolatile monomer selected from the group consisting of alkenyl aromatics, vinyl carboxylic acids, vinyl nitriles, vinyl amides, alkyl and hydroxyalkyl esters of vinyl carboxylic acids wherein the alkyl group contains from 1 to 8 carbons, and mixtures thereof, said thermosettable mixture have added thereto about 1.5 to 5 weight percent based on the weight of the mixture of an amine having the formula R1R2R3N where R1 is an alkyl or aralkyl group, R2 is hydrogen and R3 may be hydrogen or an alkyl group or R1 and R3 together may be a cyclic alkylene radical or an oxydialkylene radical; and wherein said vinyl ester resin is prepared by reacting about equivalent amounts of a polyepoxide of a polyhydric phenol having more than one epoxide group per molecule with a dicarboxylic acid half ester having the formUla
 4. The composition of claim 3 wherein and R3 in the amine formula is hydrogen. 